1. Field of the Invention
The present invention generally relates to an inductor, and more particularly, to a meander inductor structure and a substrate with the meander inductor.
2. Description of Related Art
Inductor devices have been broadly applied to a resonator, a filter or an impedance converting device. However, a small-size inductor device is usually soldered on a circuit board by using a complicate surface mounted technique (SMT). Although an inductor device today can be made in a miniature size, but the industry practice still need a plurality of inductor devices disposed on the surfaces of a multi-layers substrate, which increases the surface area and height of a solid circuit.
In order to embed an inductor device inside a multi-layers circuit substrate, many domestic or foreign developers have made an effort to make an inductor device embedded into a multi-layers PCB (printed circuit board) substrate and further applicable to various electronic circuits for years.
To design a high-frequency circuit module, the Q factor of an inductor device is a very significant parameter to affect communication quality. An inductor with a lower Q factor would reduce the overall circuit transmission efficiency. For example, when an inductor with the lower Q factor is applied to a filter of a communication system, it results in an increasing insertion loss within the filter frequency band, a broader bandwidth and introduces a greater noise. On the other hand, when an inductor with the lower Q factor is applied to an oscillator circuit, it results in an increasing output phase noise of the oscillator, which makes demodulating the modulation signal of a communication system more difficult.
In addition to the Q factor, another significant design parameter is self-resonant frequency (SRF) fr of an inductor device, in which the SRF fr restricts the operation frequency range of the inductor device. In other words, the operation frequency of the inductor device must be lower than the resonant frequency so as to keep a desirable inductor characteristic.
The U.S. Pat. No. 6,175,727 ‘Suspended Printed Inductor And LC-Type Filter Constructed Therefrom’ provides a suspended printed inductor, referring to FIG. 1, a side view diagram of a conventional suspended printed inductor. In an architecture 100, two metallic covers 110 and 120 are respectively disposed over and under a PCB 130, wherein the metallic covers 110 and 120 are grounded and enclose a suspended printed inductor 140. The suspended printed inductor 140 has two terminals 142 and 144, in which the terminal 142 is connected to an external circuit via a trace 150. In the suspended printed inductor 140 provided by the patent, the ground is located at a distance upwards or downwards from the inductor by 10 times of the substrate thickness so as to minimize a possible parasitic effect and to gain a high Q factor. FIG. 2 is a top view diagram of another conventional suspended printed inductor 200. Both the above-mentioned architectures have a major disadvantage that the process for fabricating a suspended printed inductor is more complicate than a traditional PCB process so that it is not suitable for a low-cost consumer product.
The U.S. Pat. No. 6,800,936 ‘high-frequency module device’ provides a high-frequency module device, and FIGS. 3A and 3B are respectively a sectional diagram and a top view diagram of the architecture of high-frequency module device. Referring to FIGS. 3A and 3B, a high-frequency device layer 302 is formed on a substrate 304, and the substrate 304 has a plurality of conductive layers, such as 340 and 342 etc. as shown by FIG. 3A. The high-frequency device layer 302 includes an inductor device 300, a thin film coil spiral pattern 310, an embedded conductor pattern 320 and a pullout conductor pattern 330. At the conductive layers of the substrate 304, for example, at the layers 340 and 342, wiring inhibition regions are respectively formed, and the wiring inhibition regions are located under the inductor device 300 and are not conductive. The inductor device built on a multi-layers substrate in this way, since the metal conductor under the inductor device is removed by using etching process, the parasitic effect is reduced, which is able to appropriately increase the Q factor of the inductor, and the method is similar to the traditional PCB process suitable for a low-cost commercial product.